Scots Likely to Vote For U.K. Union

Evidence of Increased Prosperity Could Swing Vote for Independence

LONDON—Most Scots will vote to keep the 308-year union with the rest of the U.K. in a referendum to be held in September, and only clear evidence that they would be financially better off is likely to produce a majority in favor of independence, according to an opinion poll published Tuesday.

The Scottish Social Attitudes survey found that 42% of the 1,497 people polled would vote to retain the union, while 20% would opt for independence. The fact that almost a third hadn't made up their minds appears to leave the outcome...